The present invention relates to a light-sensitive recording material for use in the vesicular process comprising a layer which is composed of a binder and a light-sensitive compound and is applied to a suitable support.
Recording materials for the production of vesicular images are known in the art. They comprise a layer of a thermoplastic resin and, dispersed therein, a light-sensitive compound which decomposes and generates gas when it is exposed to light. The light-sensitive layer is applied to a support. Upon exposure through an original, the light-sensitive compounds contained in the layer are decomposed according to the image of the original. The film is developed by heating it up to at least the glass transition temperature of the thermoplastic resin so that softening occurs and the photolytically produced gas which is enclosed in the binder, expands and forms bubbles. These bubbles reflect and refract light thereby making an image visible under suitable optical conditions.
It is known to use gelatin as a binder (German Pat. No. 559,795), but this has proved to be rather impractical, because although gelatin has a very high impermeability to gas, its resistance to moisture or water is extremely poor. Under the action of moisture, gelatin softens and the initially present bubbles and, consequently, also the image collapse and disappear.
Therefore, synthetic, thermoplastic, gas-tight polymers which are not sensitive to water have been disclosed for use a binders (German Pat. No. 1,155,329), but these films show, among other defects, an insufficient thermal image stability. It is also known (U.S. Pat. No. 3,161,511) to use polymethacrylonitrile as the binder in order to improve on the thermal image stability. This polymer, however, has the disadvantage of poor film forming characteristics on conventional support materials.
Further improvements of the binder materials have also been disclosed. They are directed at combining the good properties of polymethacrylonitrile, such as photographic sensitivity, with the good properties of other resins. According to U.S. Pat. No. 3,622,336 such copolymers which have thus been developed comprise, for example, different vinyl monomers which are copolymerizable with methacrylonitrile and are compatible with other organic, film-forming substances. Compared with methacrylonitrile homopolymers these vesicular materials have improved physical properties, but they do not show the high-grade utilization of gas. In addition, these systems have proved to be relatively incompatible.
The imcompatibility of methacrylonitrile copolymers in mixtures with other resins which are normally employed for the production of vesicular films is described in detail in U.S. Pat. No. 3,661,589. This patent discloses two-phase systems of hydrophobic resins which, due to the interphases present in the binder, are intended to give an increased image density. For this purpose, for example, a mixture is used of a methacrylonitrile/methylmethacrylate copolymer with an acrylonitrile/vinylidene chloride copolymer in a weight ratio of 2:1, and the incompatibility of these copolymers with one another is emphasized. The copies produced according to this teaching show an undesirably strong fogging.
It has further been attempted (German Auslegeschrift No. 2,061,464) to combine the thermal image stability of polymethacrylonitrile with the good properties, such as film formation, of other resins, for example, by copolymerizing .alpha.-chloroacrylonitrile with methacrylonitrile and/or by mixing such a copolymer with other resins. Films produced in this way show a relatively high utilization of gas, but have a marked susceptibility to scratching of the film surface, which is not acceptable in high resolution microfilms.
It is also known (German Offenlegungsschrift No. 2,044,387) to use copolymers of methacrylonitrile with ethylenically unsaturated acids, esters, nitriles or the like, as binders for the light-sensitive compound. Films produced with these binders, however, either exhibit an inferior utilization of gas or a film formation which does not meet technical requirements.
German Offenlegungsschrift No. 2,438,157 describes mixtures of polymethacrylonitrile homopolymer with other resins, for example, with a vinylidene chloride/acrylonitrile copolymer. It is pointed out that, contrary to the teachings of the prior art, compatible mixtures with other polymers can be obtained, but this compatibility can only exist within narrow limits because complicated solvent mixtures must be employed, which, in part, are toxic or very enviromentally undesirable, such as tetrahydrofuran, dioxane or acetonitrile.